1. Field of the Invention
The present invention relates generally to a head circumference adjustment device of a helmet. The adjustment device includes a main body formed with a cavity, an annular strap having a first end and a second end passing through the cavity, and a controller mounted in the cavity. Each of the first and second ends is formed with a rack sect ion, a thumb sect ion and a shoulder sect ion. The controller has a gear engaged with the rack sections of the strap. By means of rotating the controller, the position of the strap can be adjusted to adjust the head circumference. The head circumference adjustment device can be easily operated and truly fixed.
2. Description of the Related Art
A conventional helmet is formed from a blank of plastic casing. The plastic casing is fixed in a vacuum molding device and a foam material is injected into the plastic casing. After heated, the plastic casing encloses the foam material to form the helmet structure for a user to wear. In general, a hoop or a strap for adjusting the head circumference is mounted in the conventional helmet for fixing the helmet on a user's head. For example, US 2006/0225187 A1 discloses a sports helmet having a strap for adjusting the head circumference.
An upper rack section and a lower rack section are respectively disposed in the elongated closed holes of two ends of the strap. The two end sections of the strap are back and forth overlapped with each other and mounted in the case of the adjustment device to define an elongated hole with rack sections for engaging with a gear of a rotary disc. When rotating the adjustment button on the case, the gear of the rotary disc is driven to drive the annular rack sections for fastening or unfastening the strap according to the head circumference of the user.
In order to smoothly plug the two end sections (back and forth overlapped) of the strap into the case, the case is designed with a size considerably larger than the thickness or size of the two overlapped end sections of the strap. Under such circumstance, the two end sections of the strap are very likely to up and down displace within the case. As a result, the elongated hole with rack sections can be hardly accurately defined by the upper and lower rack sections. Therefore, the upper and lower rack sections can hardly stably engage with the gear of the rotary disc. When operating the rotary disc, slippage often takes place so that the position of the strap can be hardly truly adjusted and fixed.
In order to solve the above problem, some head circumference adjustment devices of helmets have been disclosed. For example, U.S. Pat. No. 8,370,967 B2 discloses an adjustable head band for a helmet. Two end sections of the band are respectively formed with an upper rack section and a lower rack section. After the upper and lower rack sections are up and down inserted into the case, the bosses in the case press the upper and lower rack sections to avoid displacement thereof. Accordingly, the upper and lower rack sections can truly define an elongated hole with rack sections.
However, as well known by those skilled in this field, the two end sections of the strap are disconnected from each other and movable relative to each other so that the strap can be fastened or unfastened by means of rotating the rotary disc. Under such circumstance, when a user operates (unfastens) the strap, the two end sections of the strap often detach out of the case of the adjustment device due to negligence. This is not what we expect.
It is therefore tried by the applicant to provide a head circumference adjustment device of a helmet to overcome the above problems existing in the prior art.
In the head circumference adjustment device of the helmet:    1. The two ends of the strap are different from the two end sections of the strap of the conventional adjustment device. It is unnecessary to back and forth overlap the two end sections of the strap to insert the two end sections into the case of the adjustment device. Accordingly, the error in adaptation of the two ends of the strap to the case can be minimized and the slippage can be avoided. Therefore, the strap can be truly adjusted.    2. The cooperation structures of the adjustment device and the strap are different from the conventional device so that in operation, the two end sections of the strap are prevented from detaching out of the case of the adjustment device due to negligence.